Wood locks up carbon – treated wood locks it up for longer

8 February 2022

COP26 Glasgow highlighted just how hard it is to get united global action on climate change. Although agreements were thin on the ground, a significant highlight of the conference was recognition for the positive role that wood plays in tackling the principal cause of global warming – carbon dioxide (CO2) emissions – and why the increased use of wood should be a key feature of strategies to decarbonise economic activity both in the UK and the world.

The world has known for some time that there are only two ways to reduce CO2 in the atmosphere

– we either reduce emissions or we capture and store it. Wood is unique

– it can do both.

Treated wood locks carbon up for longer

Man-made materials such as concrete, steel and plastic are manufactured from finite raw materials – once they’re gone, they’re gone for good. The timber on the other hand can be harvested indefinitely under sustainable forest management schemes. The more wood is used the more trees are planted. Europe’s forest areas have increased by 10% over the last 30 years, at a rate of 643 thousand hectares per year; and in North America sustainable forest management has resulted in more than 50 consecutive years where growth has exceeded harvest.

The benefit to the environment is substantial. Growing trees capture CO2 from the air and store it as carbon – typically 1 tonne of CO2 for every cubic meter of growth – while releasing 0.7 tonnes of the oxygen that is essential to life. Wood’s sustainability, carbon capture and storage ability, low energy production and sheer versatility make it a standout choice in a net-zero carbon building material strategy.

The ability to improve the durability performance of wood using modern wood protection technologies adds significantly to its versatility and efficiency. By extending the service life of wood with a preservative or wood modification process carbon is stored for a significantly longer time.

One of the most effective ways to decarbonising the built environment is to use treated wood and wood-based materials in place of ‘carbon intensive’ man-made materials like concrete, steel and plastic. A study by BRE Centre for Sustainable Products further underlines the value of treated wood in tackling climate change. The study found that a terrace made from preservative impregnated softwood had a global warming potential 200% lower than a terrace made from concrete slabs and 700% lower than composite plastic decking.

Eco-credentials of wood not compromised by treatment

BRE has also published guidance on how different design and material choices impact the environment such as the ‘Green Guide to Specification’ and ‘BREEAM’ the world’s leading sustainability assessment method for infrastructure and buildings. These publications share some key conclusions about treated wood. The first is that the wood protection process is so insignificant a factor overall as to not alter a wood product’s environmental impact rating regardless of whether it is treated or not. The second is that the use of chemically treated softwood in both structural and non-structural elements does not undermine the very strong environmental case for using wood.

In true circular bio-economic principles, when treated wood products have fulfilled their design service life they can be recovered, recycled into other applications, or used in a biofuel plant to generate heat and power.

Making the most of wood resources

Preservative pre-treatment and modified wood technologies make it possible to use lower-cost, low durability softwoods in a wide range of construction applications that would otherwise not be possible. The use of wood protection technology to deliver products with a predictable service life justifies the use of wood in the face of competition from less sustainable man-made materials.

Until now, wood protection processes have been largely viewed as optional insurance against the risk of wood decay or insect attack. But as the government’s zero carbon strategy gathers pace and British Standards adapt to warmer, wetter conditions, the building industry is likely to rely increasingly on the science of wood protection technology.

Gordon Ewbank, CEO of the WPA, says that “Influencing the Government to encourage the greater use of wood in construction is now a key priority. France has recently made it mandatory that all new public buildings are at least 50% wood. It would be good to see a similar initiative in the UK”. Gordon adds that “WPA has committed to working in collaboration with the TTF and Timber Development UK to ensure quality assured treated wood has a key place in helping to decarbonise the built environment. The time for quality treated timber is now”.